Error while loading thumbnail with mermaid/plantuml/kroki diagram

[Gsyltc]

Expected

Hi,

Since the new update (2025-11-01) I cannot load thumbnail for Mermaid or Plantmul (Kroki) Diagram.

Actual

Error

SecurityError: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.
    at HTMLImageElement.<anonymous> (structurizr-diagram-2025.11.01.js:254:41)
structurizr-diagram-2025.11.01.js:254 Uncaught SecurityError: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.
    at HTMLImageElement.<anonymous> (structurizr-diagram-2025.11.01.js:254:41)
InvalidCharacterError: Failed to execute 'btoa' on 'Window': The string to be encoded contains characters outside of the Latin1 range.
    at svgToPng (structurizr-diagram-2025.11.01.js:4960:50)
    at convertDiagramToPNG (structurizr-diagram-2025.11.01.js:4940:16)
    at Object.exportCurrentThumbnailToPNG (structurizr-diagram-2025.11.01.js:5064:13)
    at refreshThumbnail (diagrams:2132:33)
    at viewChanged (diagrams:1994:13)
    at fireViewChangedEvent (structurizr-diagram-2025.11.01.js:329:13)
    at Object.changeView (structurizr-diagram-2025.11.01.js:365:9)
    at changeView (diagrams:2657:33)
    at diagramCreated (diagrams:2555:13)

GET https://domain/workspace/1/images/XXXXXX.png 404 (Not Found)

structurizr-diagram-2025.11.01.js
254 im.dataURL = canvas.toDataURL(structurizr.constants.CONTENT_TYPE_IMAGE_PNG);

Steps to reproduce

Open Workspace, Go to Diagram :

"Message Error"
The following images/icons failed to load - please see your web browser's developer console for more details : https://kroki.mydomain/plantuml/svg/XXXXXXX

Thunbnail for non C4 diagram are not loaded.

Other information

In light mode : C4 Diagram thumbnail are loaded (and not the others)
In dark mode : C4 diagram and others are not loaded

When I click on the thumbnail, kroki (plantuml) diagram is OK.

Version/build information

Version Structurizr on-premises - 2025.11.01 AND Lite
On both version, it the same issue

Severity

Major

Priority

Low (I have no budget and there's no rush - please fix this for free)

More information

Rollback to 2025.05.28 and all is good.

[simonbrowndotje]

I think this has already been fixed (3eb9edd) but not released yet. You can build from source or use a preview build if you need this urgently.

[Gsyltc]

Hi Simon,

It's not urgent. But I will try.

Thanks for your response and your great job.